Editors Note: This is the second in a series on buying jewelry.

When shopping for gemstones, consumers need to be aware that imitation gems made of inferior stones or created in laboratories can look and feel like natural stones, but may be made from glass, plastic or synthetic material.

Lab-created and imitation stones should be clearly identified by the seller.

The buyer should also beware of treatments or enhancements to natural gems that are intended to improve their appearance or durability but may negatively affect their value. Also, the effects of some treatments may change over time and treated stones may require special care.

Some gems, for instance, can be heated to change their color or clarity. Colorless plastic or glass can be injected in others to hide cracks or fractures.

With diamonds, for example, a laser beam can be used to remove inclusions or black spots. Laser treatments are permanent and the stone does not require special care. Even though a laser-drilled diamond may appear as beautiful as an untreated stone, it may not be as valuable.

Jewelers should tell the potential buyer whether a gemstone has been treated or laser-drilled and whether the treated stone will require special care or whether the treatment significantly affected the value.

When looking at diamonds, be aware that their value is based on four criteria: color, cut, clarity, and weight. The clarity and color of a diamond are usually graded but grading scales are not uniform. A clarity grade of “slightly included” may be good quality on one scale while only fair on another. Make sure you know how scale and grade represent the color or clarity of the diamond being considered.

Diamonds and other gemstones can be measured by weight or size. Weight is measured in carats, which can be stated in fractions (such as 1/2 carat or 1/3 carat) or in decimal points. A 50 point diamond for instance weighs .50 carats or 1/2 carat. When gemstones are measured by dimensions, the size is expressed in millimeters (such as 7 x 5 millimeters).

Also be aware that imitation diamonds, like cubic zirconia, resemble diamonds but are far less costly. Lab-created gemstones, like moissanite, resemble diamonds but may not be detected by instruments used to differentiate between real diamonds and cubic zirconia. Make sure your jeweler has current testing equipment to distinguish between diamonds and other lab-created stones.

Next week: Part III, “Pearls and a Jewelry Shopper’s Checklist.”

Consumer Forum is a collaboration of the Bangor Daily News and Northeast COMBAT/The Maine Center for the Public Interest, Maine’s membership-funded nonprofit consumer organization. For help or to request individual or business membership information write: Consumer Forum, Bangor Daily News, PO Box 1329, Bangor 04402-1329.